1. Field of the Invention
The present invention relates to a plasma display apparatus and driving method thereof.
2. Background of the Related Art
In general, a plasma display panel comprises a front substrate and a rear substrate formed of soda-lime glass. Barrier ribs formed between the front substrate and the rear substrate partition discharge cells. An inert gas injected into the discharge cells, such as helium-xeon (He—Xe) or helium-neon (He—Ne), is excited with a high frequency voltage to generate a discharge. When the discharge is generated, vacuum ultraviolet rays are generated. Vacuum ultraviolet rays excite phosphors formed between the barrier ribs, thus displaying images.
FIG. 1 is a perspective view schematically showing the construction of a plasma display panel in the related art. As shown in FIG. 1, the plasma display panel in the related art comprises a front panel 10 and a rear panel 11. The front panel comprises a front glass substrate 100 and the rear panel comprises a rear glass substrate 110. The front panel 10 and the rear panel 11 are parallel to each other with a predetermined distance therebetween.
A sustain electrode pair 101, 102 for sustaining the emission of a cell through mutual discharge is formed on the front glass substrate 100. The sustain electrode pair 101, 192 comprises a scan electrode 101 and a sustain electrode 102. The scan electrode 101 comprises a transparent electrode 101a formed of a transparent ITO material and a bus electrode 101b formed of a metal material. The sustain electrode 102 comprises a transparent electrode 102a formed of a transparent ITO material and a bus electrode 102b formed of a metal material.
The scan electrode 101 receives a scan signal for scanning the panel and a sustain signal for sustaining a discharge. The sustain electrode 102 mainly receives a sustain signal. A dielectric layer 103 is formed on the sustain electrode pair 101, 102, and it functions to limit the discharge current and provides insulation between the electrode pairs. A protection layer 104 is formed on a top surface of the dielectric layer 103 and is formed of magnesium oxide (MgO) so as to facilitate a discharge condition.
Address electrodes 112 crossing the sustain electrode pair 101, 102 are disposed on the rear glass substrate 11. A dielectric layer 114 is formed on the address electrodes 112 and functions to provide insulation between the address electrodes 112. Barrier ribs 111 are formed on the dielectric layer 114 and partition discharge cells. R, G and B phosphor layers 113 are coated between the barrier ribs 111 and the barrier ribs 111 and radiate a visible ray for displaying images.
The front glass substrate 100 and the rear glass substrate 110 are adhered together by a sealing material. Inert gases, such as helium (He), neon (Ne) and xeon (Xe), are injected into the plasma display panel after an exhaust process is performed.
A method of representing gray levels of the plasma display panel constructed above will now be described with reference to FIG. 2.
FIG. 2 is a view for illustrating a method of implementing image gray levels of the plasma display panel in the related art. As shown in FIG. 2, in order to represent image gray levels of the plasma display panel in the related art, one frame is divided into several sub-fields having a different number of emissions. Each of the sub-fields is divided into a reset period for initializing all of the cells, an address period for selecting a cell to be discharged, and a sustain period for implementing gray levels depending on the number of discharges.
For example, if it is sought to display images with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields (SF1 to SF8) as shown in FIG. 2. Each of the eight sub-fields (SF1 to SF8) is again divided into a reset period, an address period and a sustain period.
The reset period and the address period of each sub-field are the same every sub-field. An address discharge for selecting a cell to be discharged is generated because of a voltage difference between the address electrodes and the scan electrodes (i.e., transparent electrodes). The sustain period is increased in the ratio of 2n (where n=0,1,2,3,4,5,6,7) in each sub-field. Since the sustain period is varied every sub-field as described above, gray levels of an image are represented by controlling the sustain period of each sub-field, i.e., a sustain discharge number.
FIG. 3 shows a driving waveform of the plasma display panel in the related art.
In the driving waveform of the plasma display panel in the related art, in the reset period, a ramp-up pulse (Ramp-up) and a ramp-down pulse (Ramp-down) are applied to the scan electrode Y. The ramp-up pulse (Ramp-up) has a waveform whose voltage rises from a sustain voltage (Vs) at a predetermined tilt. The ramp-up pulse (Ramp-up) causes a dark discharge to be generated in all of the cells of the screen. This dark discharge causes positive wall charges to be accumulated on the address electrode X and the sustain electrode Z and negative wall charges to be accumulated on the scan electrode Y.
After the ramp-up pulse (Ramp-up) is applied to the scan electrode Y, the ramp-down pulse (Ramp-down) is applied to the scan electrode Y. The ramp-down pulse (Ramp-down) has a waveform whose voltage falls from the sustain voltage (Vs) at a predetermined tilt. The ramp-down pulse (Ramp-down) causes some of wall charges, which are excessively formed within the cells, to be erased. The ramp-down pulse (Ramp-down) causes wall charges of the degree in which an address discharge can be stably generated to uniformly remain within the cells.
In the address period, while a write scan voltage (−Vyw) is applied to the scan electrode Y, a data pulse is applied to the address electrode X, so that an address discharge is generated. Furthermore, a scan voltage (Vsc) is applied to the remaining scan electrodes other than the scan electrode to which the write scan voltage (−Vyw) is applied and scan electrodes other than scan electrodes on which scanning is performed.
If the address period is finished as described above, sustain pulses are alternately applied to the scan electrode Y and the sustain electrode Z, so that, a sustain discharge is generated. In the driving waveform of the plasma display apparatus in the related art, the scan voltage (Vsc) applied to the scan electrode Y in the address period is the same in all of the sub-fields and is also the same regardless of variation in an Average Picture Level (APL) or a data load. Because the scan voltage (Vsc) is the same without regard to variation in sub-fields or a data load as described above, address margin is changed. Therefore, a problem arises because miswriting or an erroneous discharge is generated.